Method and device for configuring transmission opportunity period in wireless access system supporting unlicensed band

ABSTRACT

The present disclosure relates to a wireless access system supporting an unlicensed band, and provides a method for configuring a transmission opportunity period (TxOP) and devices for supporting the same. The method for configuring a TxOP in a wireless access system supporting an unlicensed band, according to one embodiment of the present disclosure, can comprise the steps of: performing a carrier sensing step for checking whether a secondary cell (SCell) constituted in an unlicensed band is in an idle state; transmitting a reservation signal for a predetermined amount of time if the SCell is in the idle state; and configuring a TxOP in the SCell. At this time, a start point of a first subframe (SF) included in the TxOP can be matched to a subframe, a slot or symbol boundary of a primary cell (PCell) constituted in a licensed band.

This application is a continuation application of U.S. patentapplication Ser. No. 15/328,837 filed Jan. 24, 2017, which is a NationalStage Entry of International Application No. PCT/KR2015/008052 filedJul. 31, 2015, which claims priority to U.S. Provisional ApplicationNos. 62/031,817 filed Jul. 31, 2014; 62/081,562 filed Nov. 18, 2014;62/105,754 filed Jan. 21, 2015; 62/132,511 filed Mar. 13, 2015;62/142,448 filed Apr. 2, 2015 and 62/166,122 filed May 25, 2015, all ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a wireless access systemsupporting an unlicensed band, and more particularly, to a method forconfiguring a Transmission Opportunity Period (TxOP) and an apparatussupporting the same.

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, and a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system.

DISCLOSURE Technical Problem

An object of the present disclosure is to provide a method forefficiently transmitting and receiving data in a wireless access systemsupporting an unlicensed band.

Another object of the present disclosure is to provide various methodsfor configuring a Transmission Opportunity Period (TxOP) and apparatusessupporting the same in a wireless access system supporting an unlicensedband.

Another object of the present disclosure is to provide, if a TxOPincludes a subframe having a different size from the size of a subframeof a primacy cell (PCell), a method for determining the subframe havinga different size, and methods for determining a Transport Block Size(TBS) and configuring a Reference Signal (RS) for the subframe having adifferent size.

Another object of the present disclosure is to provide, if TxOPs areconsecutively configured, methods for configuring a timing gap and/ortransmitting a reservation signal without wasting subframes.

Another object of the present disclosure is to provide apparatusessupporting the above methods.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The present disclosure relates to a wireless access system supporting anunlicensed band. More particularly, the present disclosure provides amethod for configuring a Transmission Opportunity Period (TxOP), andapparatuses supporting the same.

In an aspect of the present disclosure, provided herein is a method forconfiguring a TxOP in a wireless access system supporting an unlicensedband, including performing a carrier sensing (CS) procedure to determinewhether a secondary cell (SCell) configured in the unlicensed band isidle, if the SCell is idle, transmitting a reservation signal during apredetermined time, and configuring a TxOP in the SCell. A starting timeof a first subframe (SF) of the TxOP is aligned with an SF boundary,slot boundary, or symbol boundary of a primary cell (PCell) configuredin a licensed band.

In another aspect of the present disclosure, an apparatus forconfiguring a TxOP in a wireless access system supporting an unlicensedband includes a transmitter, a receiver, and a processor configured tosupport a TxOP configuration. The processor is configured to perform aCS procedure to determine whether an SCell configured in the unlicensedband is idle by controlling the transmitter and the receiver, totransmit, if the SCell is idle, a reservation signal during apredetermined time by controlling the transmitter, and to configure aTxOP in the SCell. A starting time of a first SF of the TxOP is alignedwith an SF boundary, slot boundary, or symbol boundary of a PCellconfigured in a licensed band.

In the aspects of the present disclosure, if it is said that an SCell isidle, this means that the SCell is not occupied by CS. In other words,the SCell is finally idle, upon completion of a CS procedure including abackoff operation or an LBT operation.

If the starting time of the first SF is aligned with a slot boundary ofthe PCell, the reservation signal may be transmitted until before thestarting time of the first SF after the CS procedure.

If the starting time of the first SF is aligned with a slot boundary orsymbol boundary of the PCell, the first SF is configured as a partial SF(pSF) having a smaller length than an SF of the PCell.

If one SF is divided into T points and the first SF starts at a k^(th)point among the T points, the number N_(PRB) of physical resource blocks(PRBs) in the first SF may be calculated by the following equation.

$\begin{matrix}{N_{PRB} = {\max\left\{ {\left\lfloor {N_{PRB}^{\prime} \times \frac{k}{T}} \right\rfloor,1} \right\}}} & \lbrack{Equation}\rbrack\end{matrix}$

Herein, N′_(PRB) represents a total number of allocated PRBs, and k andT are positive integers.

A demodulation reference signal (DM-RS) transmitted in the first SF maybe allocated only to a second slot in which the first SF is configured.

If the starting time of the first SF is aligned with a symbol boundaryof the PCell, it may be determined whether the first SF is configuredindependently, or concatenated to a next SF into an over SF (oSF), basedon a threshold set as a number of OFDM symbols.

If the first SF is configured to be an oSF, one SF is divided into Tpoints, and the first SF starts at a k^(th) point among the T points,the number N_(PRB) of PRBs in the first SF may be calculated by thefollowing equation.

$\begin{matrix}{N_{PRB} = {\max\left\{ {\left\lfloor {N_{PRB}^{\prime} \times \frac{T + k}{T}} \right\rfloor,1} \right\}}} & \lbrack{Equation}\rbrack\end{matrix}$

Herein, N′_(PRB) represents a total number of allocated PRBs, and k andT are positive integers.

If the first SF is configured to be an oSF, one SF is divided into Tpoints, and the first SF starts at a k^(th) point among the T points,the number N_(PRB) of PRBs in the first SF may be calculated by thefollowing equation.

$\begin{matrix}{{{TBS}\left( {I_{TBS},N_{PRB}} \right)} = \left\lfloor {{{TBS}\left( {I_{TBS},N_{PRB}^{\prime}} \right)} \times \frac{T + k}{T}} \right\rfloor} & \lbrack{Equation}\rbrack\end{matrix}$

Herein, N′_(PRB) represents a total number of allocated PRBs, I_(TBS)represents an index indicating a transport block size (TBS) for thefirst SF, and k and T are positive integers.

If the first SF is configured to be an oSF, a DM-RS transmitted in thefirst SF may be allocated only within the concatenated next SF.

If two or more TxOPs are configured consecutively, a first SF of each ofthe TxOPs may be configured to have a fixed length smaller than a lengthof one SF. Herein, a specific timing gap may be configured before asecond TxOP starts after the end of the first TxOP among the consecutiveTxOPs.

It is to be understood that both the foregoing general description andthe following detailed description of the present disclosure areexemplary and explanatory and are intended to provide furtherexplanation of the disclosure as claimed.

Advantageous Effects

As is apparent from the above description, the embodiments of thepresent disclosure have the following effects.

First, data can be efficiently transmitted and received in a wirelessaccess system supporting an unlicensed band.

Secondly, various methods for configuring a Transmission OpportunityPeriod (TxOP) and apparatuses supporting the same in a wireless accesssystem supporting an unlicensed band can be provided.

Thirdly, if a TxOP includes a subframe having a different size from thesize of a subframe of a primacy cell (PCell), a method for determiningthe subframe having a different size, and methods for determining aTransport Block Size (TBS) and configuring a Reference Signal (RS) forthe subframe having a different size can be provided.

Fourthly, if TxOPs are consecutively configured, a timing gap and/or areservation signal may be configured and transmitted without wastingsubframes.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present disclosurewithout departing from the technical features or scope of thedisclosures. Thus, it is intended that the present disclosure covers themodifications and variations of this disclosure provided they comewithin the scope of the appended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure, illustrate embodiments of thedisclosure and together with the description serve to explain theprinciple of the disclosure. In the drawings:

FIG. 1 is a view illustrating physical channels and a signaltransmission method using the physical channels;

FIG. 2 is a view illustrating exemplary radio frame structures;

FIG. 3 is a view illustrating an exemplary resource grid for theduration of a downlink slot;

FIG. 4 is a view illustrating an exemplary structure of an uplinksubframe;

FIG. 5 is a view illustrating an exemplary structure of a downlinksubframe;

FIG. 6 is a view illustrating an example of Component Carriers (CCs) andCarrier Aggregation (CA) in a Long Term Evolution-Advanced (LTE-A)system;

FIG. 7 is a view illustrating a subframe structure based oncross-carrier scheduling in the LTE-A system;

FIG. 8 is a view illustrating an exemplary serving cell configurationbased on cross-carrier scheduling;

FIG. 9 is a conceptual view of a Coordinated Multi-Point (CoMP) systemoperating in a CA environment;

FIG. 10 is a view illustrating an exemplary subframe to whichUE-specific Reference Signals (UE-RSs) are allocated, which may be usedin embodiments of the present disclosure;

FIG. 11 is a view illustrating exemplary multiplexing of legacy PhysicalDownlink Control Channel (PDCCH), Physical Downlink Shared Channel(PDSCH), and Evolved-PDCCH (E-PDCCH) in an LTE/LTE-A system;

FIG. 12 is a view illustrating an exemplary CA environment supported inan LTE-Unlicensed (LTE-U) system;

FIG. 13 is a view illustrating an exemplary Frame Based Equipment (FBE)operation as one of Listen-Before-Talk (LBT) operations;

FIG. 14 is a block diagram illustrating the FBE operation;

FIG. 15 is a view illustrating an exemplary Load Based Equipment (LBE)operation as one of the LBT operations;

FIGS. 16 and 17 are views illustrating a method for transmitting areservation signal;

FIG. 18 is a view illustrating an embodiment of setting a maximum valuefor a reservation signal transmission period;

FIG. 19 is a view illustrating a method for adjusting the starting timeof a SubFrame (SF) in a Secondary Cell (SCell) according to an operationof a Primary Cell (PCell);

FIG. 20 is a view illustrating a method for aligning an SF boundary ofan SCell with a slot boundary of a PCell;

FIG. 21 is a view illustrating configurations of Reference Signals (RSs)transmitted in an SCell;

FIG. 22 is a view illustrating a method for determining an SF lengthbased on a threshold;

FIG. 23 is a view illustrating a method for fixing the length of thefirst SF of a Transmission Opportunity Period (TxOP);

FIG. 24 is a view illustrating a method for allocating DemodulationReference Signals (DM-RSs), if the last SF of a TxOP is configuredvariably;

FIG. 25 is a view illustrating a case of fixing the length of the firstSF of a TxOP;

FIG. 26 is a view illustrating one of methods for configuring the firstand last SFs of a TxOP based on a threshold;

FIG. 27 is a view illustrating another of the methods for transmitting areservation signal based on a threshold;

FIG. 28 is a view illustrating a method for transmitting a reservationsignal;

FIG. 29 is a view illustrating a TxOP configuration, if the first SF ofa TxOP is aligned with a slot boundary;

FIG. 30 is a view illustrating one of methods for configuringconsecutive TxOPs;

FIG. 31 is a flowchart illustrating one of methods for transmitting andreceiving data according to a TxOP configuration; and

FIG. 32 is a block diagram of apparatuses for implementing the methodsillustrated in FIGS. 1 to 31.

BEST MODE FOR CARRYING OUT THE DISCLOSURE

Embodiments of the present disclosure as described below in detailrelate to a wireless access system supporting an unlicensed band, andprovide a method for configuring a Transmission Opportunity Period(TxOP) and apparatuses supporting the same.

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a or an”, “one”, “the” etc. may include a singularrepresentation and a plural representation in the context of the presentdisclosure (more particularly, in the context of the following claims)unless indicated otherwise in the specification or unless contextclearly indicates otherwise.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a BaseStation (BS) and a User Equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a Mobile Station (MS), a Subscriber Station (SS), aMobile Subscriber Station (MSS), a mobile terminal, an Advanced MobileStation (AMS), etc.

A transmission end is a fixed and/or mobile node that provides a dataservice or a voice service and a reception end is a fixed and/or mobilenode that receives a data service or a voice service. Therefore, a UEmay serve as a transmission end and a BS may serve as a reception end,on an UpLink (UL). Likewise, the UE may serve as a reception end and theBS may serve as a transmission end, on a DownLink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3rd Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present disclosure may be supportedby the standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, 3GPP TS 36.321 and 3GPP TS 36.331. That is, the steps or parts,which are not described to clearly reveal the technical idea of thepresent disclosure, in the embodiments of the present disclosure may beexplained by the above standard specifications. All terms used in theembodiments of the present disclosure may be explained by the standardspecifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the disclosure.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical spirit andscope of the present disclosure.

For example, the term, TxOP may be used interchangeably withtransmission period or Reserved Resource Period (RRP) in the same sense.Further, a Listen-Before-Talk (LBT) procedure may be performed for thesame purpose as a carrier sensing procedure for determining whether achannel state is idle or busy.

Hereinafter, 3GPP LTE/LTE-A systems are explained, which are examples ofwireless access systems.

The embodiments of the present disclosure can be applied to variouswireless access systems such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present disclosure are described inthe context of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present disclosure, the present disclosure is alsoapplicable to an IEEE 802.16e/m system, etc.

1.3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

1.1 System Overview

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels, which may be used in embodiments ofthe present disclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell Identifier (ID) byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB.

During the initial cell search, the UE may monitor a DL channel state byreceiving a Downlink Reference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a Physical Random Access Channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a Physical Uplink Shared Channel (PUSCH)and/or a Physical Uplink Control Channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled Uplink Control Information (UCI). The UCI includes a HybridAutomatic Repeat and reQuest Acknowledgement/Negative Acknowledgement(HARQ-ACK/NACK), a Scheduling Request (SR), a Channel Quality Indicator(CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2 illustrates exemplary radio frame structures used in embodimentsof the present disclosure.

FIG. 2(a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full Frequency Division Duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (Tf=307200·Ts) long, including equal-sized 20slots indexed from 0 to 19. Each slot is 0.5 ms (Tslot=15360·Ts) long.One subframe includes two successive slots. An ith subframe includes2ith and (2i+1)th slots. That is, a radio frame includes 10 subframes. Atime required for transmitting one subframe is defined as a TransmissionTime Interval (TTI). Ts is a sampling time given as Ts=1/(15kHz×2048)=3.2552×10−8 (about 33 ns). One slot includes a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbols or SC-FDMAsymbols in the time domain by a plurality of Resource Blocks (RBs) inthe frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2(b) illustrates frame structure type 2. Frame structure type 2 isapplied to a Time Division Duplex (TDD) system. One radio frame is 10 ms(Tf=307200·Ts) long, including two half-frames each having a length of 5ms (=153600·Ts) long. Each half-frame includes five subframes each being1 ms (=30720·Ts) long. An ith subframe includes 2ith and (2i+1)th slotseach having a length of 0.5 ms (Tslot=15360·Ts). Ts is a sampling timegiven as Ts=1/(15 kHz×2048)=3.2552×10−8 (about 33 ns).

A type-2 frame includes a special subframe having three fields, DownlinkPilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink UpPTS Extended cyclic prefix indownlink Normal Extended UpPTS Special subframe cyclic prefix cyclicprefix Normal cyclic Extended cyclic configuration DwPTS in uplink inuplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s) 2192 ·T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentdisclosure.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent disclosure is not limited.

Each element of the resource grid is referred to as a Resource Element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, NDLdepends on a DL transmission bandwidth. A UL slot may have the samestructure as a DL slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present disclosure.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe are allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present disclosure.

Referring to FIG. 5, up to three OFDM symbols of a DL subframe, startingfrom OFDM symbol 0 are used as a control region to which controlchannels are allocated and the other OFDM symbols of the DL subframe areused as a data region to which a PDSCH is allocated. DL control channelsdefined for the 3GPP LTE system include a Physical Control FormatIndicator Channel (PCFICH), a PDCCH, and a Physical Hybrid ARQ IndicatorChannel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called Downlink Control Information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL Transmission (Tx) power control commands for a UE group.

1.2 Physical Downlink Control Channel (PDCCH)

1.2.1 PDCCH Overview

The PDCCH may deliver information about resource allocation and atransport format for a Downlink Shared Channel (DL-SCH) (i.e. a DLgrant), information about resource allocation and a transport format foran Uplink Shared Channel (UL-SCH) (i.e. a UL grant), paging informationof a Paging Channel (PCH), system information on the DL-SCH, informationabout resource allocation for a higher-layer control message such as arandom access response transmitted on the PDSCH, a set of Tx powercontrol commands for individual UEs of a UE group, Voice Over InternetProtocol (VoIP) activation indication information, etc.

A plurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted in an aggregate ofone or more consecutive Control Channel Elements (CCEs). A PDCCH made upof one or more consecutive CCEs may be transmitted in the control regionafter subblock interleaving. A CCE is a logical allocation unit used toprovide a PDCCH at a code rate based on the state of a radio channel ACCE includes a plurality of RE Groups (REGs). The format of a PDCCH andthe number of available bits for the PDCCH are determined according tothe relationship between the number of CCEs and a code rate provided bythe CCEs.

1.2.2 PDCCH Structure

A plurality of PDCCHs for a plurality of UEs may be multiplexed andtransmitted in the control region. A PDCCH is made up of an aggregate ofone or more consecutive CCEs. A CCE is a unit of 9 REGs each REGincluding 4 REs. Four Quadrature Phase Shift Keying (QPSK) symbols aremapped to each REG. REs occupied by RSs are excluded from REGs. That is,the total number of REGs in an OFDM symbol may be changed depending onthe presence or absence of a cell-specific RS. The concept of an REG towhich four REs are mapped is also applicable to other DL controlchannels (e.g. the PCFICH or the PHICH). Let the number of REGs that arenot allocated to the PCFICH or the PHICH be denoted by NREG. Then thenumber of CCEs available to the system is NCCE (=└N_(REG)/9┘) and theCCEs are indexed from 0 to NCCE-1.

To simplify the decoding process of a UE, a PDCCH format including nCCEs may start with a CCE having an index equal to a multiple of n. Thatis, given CCE i, the PDCCH format may start with a CCE satisfying i modn=0.

The eNB may configure a PDCCH with 1, 2, 4, or 8 CCEs. {1, 2, 4, 8} arecalled CCE aggregation levels. The number of CCEs used for transmissionof a PDCCH is determined according to a channel state by the eNB. Forexample, one CCE is sufficient for a PDCCH directed to a UE in a good DLchannel state (a UE near to the eNB). On the other hand, 8 CCEs may berequired for a PDCCH directed to a UE in a poor DL channel state (a UEat a cell edge) in order to ensure sufficient robustness.

[Table 2] below illustrates PDCCH formats. 4 PDCCH formats are supportedaccording to CCE aggregation levels as illustrated in [Table 2].

TABLE 2 Number of PDCCH format Number of CCE (n) Number of REG PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

A different CCE aggregation level is allocated to each UE because theformat or Modulation and Coding Scheme (MCS) level of controlinformation delivered in a PDCCH for the UE is different. An MCS leveldefines a code rate used for data coding and a modulation order. Anadaptive MCS level is used for link adaptation. In general, three orfour MCS levels may be considered for control channels carrying controlinformation.

Regarding the formats of control information, control informationtransmitted on a PDCCH is called DCI. The configuration of informationin PDCCH payload may be changed depending on the DCI format. The PDCCHpayload is information bits. [Table 3] lists DCI according to DCIformats.

TABLE 3 DCI Format Description Format 0 Resource grants for PUSCHtransmissions (uplink) Format 1 Resource assignments for single codewordPDSCH transmission (transmission modes 1, 2 and 7) Format 1A Compactsignaling of resource assignments for single codeword PDSCH (all modes)Format 1B Compact resource assignments for PDSCH using rank-1 closedloop precoding (mode 6) Format 1C Very compact resource assignments forPDSCH (e.g., paging/broadcast system information) Format 1D Compactresource assignments for PDSCH using multi-user MIMO (mode 5) Format 2Resource assignments for PDSCH for closed loop MIMO operation (mode 4)Format 2A resource assignments for PDSCH for open loop MIMO operation(mode 3) Format 3/3A Power control commands for PUCCH and PUSCH with2-bit/1-bit power adjustment Format 4 Scheduling of PUSCH in one UL cellwith multi-antenna port transmission mode

Referring to [Table 3], the DCI formats include Format 0 for PUSCHscheduling, Format 1 for single-codeword PDSCH scheduling, Format 1A forcompact single-codeword PDSCH scheduling, Format 1C for very compactDL-SCH scheduling, Format 2 for PDSCH scheduling in a closed-loopspatial multiplexing mode, Format 2A for PDSCH scheduling in anopen-loop spatial multiplexing mode, and Format 3/3A for transmission ofTransmission Power Control (TPC) commands for uplink channels. DCIFormat 1A is available for PDSCH scheduling irrespective of thetransmission mode of a UE.

The length of PDCCH payload may vary with DCI formats. In addition, thetype and length of PDCCH payload may be changed depending on compact ornon-compact scheduling or the transmission mode of a UE.

The transmission mode of a UE may be configured for DL data reception ona PDSCH at the UE. For example, DL data carried on a PDSCH includesscheduled data, a paging message, a random access response, broadcastinformation on a BCCH, etc. for a UE. The DL data of the PDSCH isrelated to a DCI format signaled through a PDCCH. The transmission modemay be configured semi-statically for the UE by higher-layer signaling(e.g. Radio Resource Control (RRC) signaling). The transmission mode maybe classified as single antenna transmission or multi-antennatransmission.

A transmission mode is configured for a UE semi-statically byhigher-layer signaling. For example, multi-antenna transmission schememay include transmit diversity, open-loop or closed-loop spatialmultiplexing, Multi-User Multiple Input Multiple Output (MU-MIMO), orbeamforming. Transmit diversity increases transmission reliability bytransmitting the same data through multiple Tx antennas. Spatialmultiplexing enables high-speed data transmission without increasing asystem bandwidth by simultaneously transmitting different data throughmultiple Tx antennas. Beamforming is a technique of increasing theSignal to Interference plus Noise Ratio (SINR) of a signal by weightingmultiple antennas according to channel states.

A DCI format for a UE depends on the transmission mode of the UE. The UEhas a reference DCI format monitored according to the transmission modeconfigure for the UE. The following 10 transmission modes are availableto UEs:

(1) Transmission mode 1: Single antenna port (port 0);

(2) Transmission mode 2: Transmit diversity;

(3) Transmission mode 3: Open-loop spatial multiplexing when the numberof layer is larger than 1 or Transmit diversity when the rank is 1;

(4) Transmission mode 4: Closed-loop spatial multiplexing;

(5) Transmission mode 5: MU-MIMO;

(6) Transmission mode 6: Closed-loop rank-1 precoding;

(7) Transmission mode 7: Precoding supporting a single layertransmission, which is not based on a codebook (Rel-8);

(8) Transmission mode 8: Precoding supporting up to two layers, whichare not based on a codebook (Rel-9);

(9) Transmission mode 9: Precoding supporting up to eight layers, whichare not based on a codebook (Rel-10); and

(10) Transmission mode 10: Precoding supporting up to eight layers,which are not based on a codebook, used for CoMP (Rel-11).

1.2.3 PDCCH Transmission

The eNB determines a PDCCH format according to DCI that will betransmitted to the UE and adds a Cyclic Redundancy Check (CRC) to thecontrol information. The CRC is masked by a unique Identifier (ID) (e.g.a Radio Network Temporary Identifier (RNTI)) according to the owner orusage of the PDCCH. If the PDCCH is destined for a specific UE, the CRCmay be masked by a unique ID (e.g. a cell-RNTI (C-RNTI)) of the UE. Ifthe PDCCH carries a paging message, the CRC of the PDCCH may be maskedby a paging indicator ID (e.g. a Paging-RNTI (P-RNTI)). If the PDCCHcarries system information, particularly, a System Information Block(SIB), its CRC may be masked by a system information ID (e.g. a SystemInformation RNTI (SI-RNTI)). To indicate that the PDCCH carries a randomaccess response to a random access preamble transmitted by a UE, its CRCmay be masked by a Random Access-RNTI (RA-RNTI).

Then, the eNB generates coded data by channel-encoding the CRC-addedcontrol information. The channel coding may be performed at a code ratecorresponding to an MCS level. The eNB rate-matches the coded dataaccording to a CCE aggregation level allocated to a PDCCH format andgenerates modulation symbols by modulating the coded data. Herein, amodulation order corresponding to the MCS level may be used for themodulation. The CCE aggregation level for the modulation symbols of aPDCCH may be one of 1, 2, 4, and 8. Subsequently, the eNB maps themodulation symbols to physical REs (i.e. CCE to RE mapping).

1.2.4 Blind Decoding (BD)

A plurality of PDCCHs may be transmitted in a subframe. That is, thecontrol region of a subframe includes a plurality of CCEs, CCE 0 to CCEN_(CCE,k-1). N_(CCE,k) is the total number of CCEs in the control regionof a kth subframe. A UE monitors a plurality of PDCCHs in everysubframe. This means that the UE attempts to decode each PDCCH accordingto a monitored PDCCH format.

The eNB does not provide the UE with information about the position of aPDCCH directed to the UE in an allocated control region of a subframe.Without knowledge of the position, CCE aggregation level, or DCI formatof its PDCCH, the UE searches for its PDCCH by monitoring a set of PDCCHcandidates in the subframe in order to receive a control channel fromthe eNB. This is called blind decoding. Blind decoding is the process ofdemasking a CRC part with a UE ID, checking a CRC error, and determiningwhether a corresponding PDCCH is a control channel directed to a UE bythe UE.

The UE monitors a PDCCH in every subframe to receive data transmitted tothe UE in an active mode. In a Discontinuous Reception (DRX) mode, theUE wakes up in a monitoring interval of every DRX cycle and monitors aPDCCH in a subframe corresponding to the monitoring interval. ThePDCCH-monitored subframe is called a non-DRX subframe.

To receive its PDCCH, the UE should blind-decode all CCEs of the controlregion of the non-DRX subframe. Without knowledge of a transmitted PDCCHformat, the UE should decode all PDCCHs with all possible CCEaggregation levels until the UE succeeds in blind-decoding a PDCCH inevery non-DRX subframe. Since the UE does not know the number of CCEsused for its PDCCH, the UE should attempt detection with all possibleCCE aggregation levels until the UE succeeds in blind decoding of aPDCCH.

In the LTE system, the concept of Search Space (SS) is defined for blinddecoding of a UE. An SS is a set of PDCCH candidates that a UE willmonitor. The SS may have a different size for each PDCCH format. Thereare two types of SSs, Common Search Space (CSS) andUE-specific/Dedicated Search Space (USS).

While all UEs may know the size of a CSS, a USS may be configured foreach individual UE. Accordingly, a UE should monitor both a CSS and aUSS to decode a PDCCH. As a consequence, the UE performs up to 44 blinddecodings in one subframe, except for blind decodings based on differentCRC values (e.g., C-RNTI, P-RNTI, SI-RNTI, and RA-RNTI).

In view of the constraints of an SS, the eNB may not secure CCEresources to transmit PDCCHs to all intended UEs in a given subframe.This situation occurs because the remaining resources except forallocated CCEs may not be included in an SS for a specific UE. Tominimize this obstacle that may continue in the next subframe, aUE-specific hopping sequence may apply to the starting point of a USS.

[Table 4] illustrates the sizes of CSSs and USSs.

TABLE 4 PDCCH Number of Number of Number of Format CCE (n) candidates inCSS candidates in USS 0 1 — 6 1 2 — 6 2 4 4 2 3 8 2 2

To mitigate the load of the UE caused by the number of blind decodingattempts, the UE does not search for all defined DCI formatssimultaneously. Specifically, the UE always searches for DCI Format 0and DCI Format 1A in a USS. Although DCI Format 0 and DCI Format 1A areof the same size, the UE may distinguish the DCI formats by a flag forformat0/format 1a differentiation included in a PDCCH. Other DCI formatsthan DCI Format 0 and DCI Format 1A, such as DCI Format 1, DCI Format1B, and DCI Format 2 may be required for the UE.

The UE may search for DCI Format 1A and DCI Format 1C in a CSS. The UEmay also be configured to search for DCI Format 3 or 3A in the CSS.Although DCI Format 3 and DCI Format 3A have the same size as DCI Format0 and DCI Format 1A, the UE may distinguish the DCI formats by a CRCscrambled with an ID other than a UE-specific ID.

An SS S_(k) ^((L)) is a PDCCH candidate set with a CCE aggregation levelL∈{1,2,4,8}. The CCEs of PDCCH candidate set m in the SS may bedetermined by the following equation.L·{(Y _(k) +m)mod └N_(CCE,k) /L┘}+i  [Equation 1]

Herein, M^((L)) is the number of PDCCH candidates with CCE aggregationlevel L to be monitored in the SS, m=0, . . . , M^((L))−1, i is theindex of a CCE in each PDCCH candidate, and i=0, . . . , L−1.k=└n_(s)/2┘ where n_(s) is the index of a slot in a radio frame.

As described before, the UE monitors both the USS and the CSS to decodea PDCCH. The CSS supports PDCCHs with CCE aggregation levels {4, 8} andthe USS supports PDCCHs with CCE aggregation levels {1, 2, 4, 8}. [Table5] illustrates PDCCH candidates monitored by a UE.

TABLE 5 Search space S_(k) ^((L)) Number of PDCCH Type Aggregation levelL Size [in CCEs] candidates M^((L)) UE- 1 6 6 specific 2 12 6 4 8 2 8 162 Common 4 16 4 8 16 2

Referring to [Equation 1], for two aggregation levels, L=4 and L=8,Y_(k) is set to 0 in the CSS, whereas Y_(k) is defined by [Equation 2]for aggregation level L in the USS.Y _(k)=(A·Y _(k-1))mod D  [Equation 2]

Herein, Y⁻¹=n_(RNTI)≠0, n_(RNTI) indicating an RNTI value. A=39827 andD=65537.

2. Carrier Aggregation (CA) Environment

2.1 CA Overview

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present disclosure, multi-carrier means CA (or carriercombining). Herein, CA covers aggregation of contiguous carriers andaggregation of non-contiguous carriers. The number of aggregated CCs maybe different for a DL and a UL. If the number of DL CCs is equal to thenumber of UL CCs, this is called symmetric aggregation. If the number ofDL CCs is different from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent disclosure may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher-layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher-layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present disclosure.

FIG. 6 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure.

FIG. 6(a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 6(b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 6(b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≤N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≤M≤N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher-layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by System Information Block Type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

2.2 Cross Carrier Scheduling

Two scheduling schemes, self-scheduling and cross carrier scheduling aredefined for a CA system, from the perspective of carriers or servingcells. Cross carrier scheduling may be called cross CC scheduling orcross cell scheduling.

In self-scheduling, a PDCCH (carrying a DL grant) and a PDSCH aretransmitted in the same DL CC or a PUSCH is transmitted in a UL CClinked to a DL CC in which a PDCCH (carrying a UL grant) is received.

In cross carrier scheduling, a PDCCH (carrying a DL grant) and a PDSCHare transmitted in different DL CCs or a PUSCH is transmitted in a UL CCother than a UL CC linked to a DL CC in which a PDCCH (carrying a ULgrant) is received.

Cross carrier scheduling may be activated or deactivated UE-specificallyand indicated to each UE semi-statically by higher-layer signaling (e.g.RRC signaling).

If cross carrier scheduling is activated, a Carrier Indicator Field(CIF) is required in a PDCCH to indicate a DL/UL CC in which aPDSCH/PUSCH indicated by the PDCCH is to be transmitted. For example,the PDCCH may allocate PDSCH resources or PUSCH resources to one of aplurality of CCs by the CIF. That is, when a PDCCH of a DL CC allocatesPDSCH or PUSCH resources to one of aggregated DL/UL CCs, a CIF is set inthe PDCCH. In this case, the DCI formats of LTE Release-8 may beextended according to the CIF. The CIF may be fixed to three bits andthe position of the CIF may be fixed irrespective of a DCI format size.In addition, the LTE Release-8 PDCCH structure (the same coding andresource mapping based on the same CCEs) may be reused.

On the other hand, if a PDCCH transmitted in a DL CC allocates PDSCHresources of the same DL CC or allocates PUSCH resources in a single ULCC linked to the DL CC, a CIF is not set in the PDCCH. In this case, theLTE Release-8 PDCCH structure (the same coding and resource mappingbased on the same CCEs) may be used.

If cross carrier scheduling is available, a UE needs to monitor aplurality of PDCCHs for DCI in the control region of a monitoring CCaccording to the transmission mode and/or bandwidth of each CC.Accordingly, an appropriate SS configuration and PDCCH monitoring areneeded for the purpose.

In the CA system, a UE DL CC set is a set of DL CCs scheduled for a UEto receive a PDSCH, and a UE UL CC set is a set of UL CCs scheduled fora UE to transmit a PUSCH. A PDCCH monitoring set is a set of one or moreDL CCs in which a PDCCH is monitored. The PDCCH monitoring set may beidentical to the UE DL CC set or may be a subset of the UE DL CC set.The PDCCH monitoring set may include at least one of the DL CCs of theUE DL CC set. Or the PDCCH monitoring set may be defined irrespective ofthe UE DL CC set. DL CCs included in the PDCCH monitoring set may beconfigured to always enable self-scheduling for UL CCs linked to the DLCCs. The UE DL CC set, the UE UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

If cross carrier scheduling is deactivated, this implies that the PDCCHmonitoring set is always identical to the UE DL CC set. In this case,there is no need for signaling the PDCCH monitoring set. However, ifcross carrier scheduling is activated, the PDCCH monitoring set may bedefined within the UE DL CC set. That is, the eNB transmits a PDCCH onlyin the PDCCH monitoring set to schedule a PDSCH or PUSCH for the UE.

FIG. 7 illustrates a cross carrier-scheduled subframe structure in theLTE-A system, which is used in embodiments of the present disclosure.

Referring to FIG. 7, three DL CCs are aggregated for a DL subframe forLTE-A UEs. DL CC ‘A’ is configured as a PDCCH monitoring DL CC. If a CIFis not used, each DL CC may deliver a PDCCH that schedules a PDSCH inthe same DL CC without a CIF. On the other hand, if the CIF is used byhigher-layer signaling, only DL CC ‘A’ may carry a PDCCH that schedulesa PDSCH in the same DL CC ‘A’ or another CC. Herein, no PDCCH istransmitted in DL CC ‘B’ and DL CC ‘C’ that are not configured as PDCCHmonitoring DL CCs.

FIG. 8 is conceptual diagram illustrating a construction of servingcells according to cross-carrier scheduling.

Referring to FIG. 8, an eNB (or BS) and/or UEs for use in a radio accesssystem supporting carrier aggregation (CA) may include one or moreserving cells. In FIG. 8, the eNB can support a total of four servingcells (cells A, B, C and D). It is assumed that UE A may include Cells(A, B, C), UE B may include Cells (B, C, D), and UE C may include CellB. In this case, at least one of cells of each UE may be composed ofPCell. In this case, PCell is always activated, and SCell may beactivated or deactivated by the eNB and/or UE.

The cells shown in FIG. 8 may be configured per UE. The above-mentionedcells selected from among cells of the eNB, cell addition may be appliedto carrier aggregation (CA) on the basis of a measurement report messagereceived from the UE. The configured cell may reserve resources forACK/NACK message transmission in association with PDSCH signaltransmission. The activated cell is configured to actually transmit aPDSCH signal and/or a PUSCH signal from among the configured cells, andis configured to transmit CSI reporting and Sounding Reference Signal(SRS) transmission. The deactivated cell is configured not totransmit/receive PDSCH/PUSCH signals by an eNB command or a timeroperation, and CRS reporting and SRS transmission are interrupted.

2.3 CA Environment-Based CoMP Operation

Hereinafter, a cooperation multi-point (CoMP) transmission operationapplicable to the embodiments of the present disclosure will bedescribed.

In the LTE-A system, CoMP transmission may be implemented using acarrier aggregation (CA) function in the LTE. FIG. 9 is a conceptualview illustrating a CoMP system operating based on a CA environment.

In FIG. 9, it is assumed that a carrier operated as a PCell and acarrier operated as an SCell may use the same frequency band on afrequency axis and are allocated to two eNBs geographically spaced apartfrom each other. At this time, a serving eNB of UE1 may be allocated tothe PCell, and a neighboring cell causing much interference may beallocated to the SCell. That is, the eNB of the PCell and the eNB of theSCell may perform various DL/UL CoMP operations such as jointtransmission (JT), CS/CB and dynamic cell selection for one UE.

FIG. 9 illustrates an example that cells managed by two eNBs areaggregated as PCell and SCell with respect to one UE (e.g., UE1).However, as another example, three or more cells may be aggregated. Forexample, some cells of three or more cells may be configured to performCoMP operation for one UE in the same frequency band, and the othercells may be configured to perform simple CA operation in differentfrequency bands. At this time, the PCell does not always need toparticipate in CoMP operation.

2.4 Reference Signal (RS)

Now, a description will be given of RSs which may be used in embodimentsof the present disclosure.

FIG. 10 illustrates an example of a subframe to which UE-RSs areallocated, which may be used in embodiments of the present disclosure.

Referring to FIG. 10, the subframe illustrates REs occupied by UE-RSsamong REs in one RB of a normal DL subframe having a normal CP.

UE-RSs are transmitted on antenna port(s) p=5, p=7, p=8 or p=7, 8, . . ., ν+6 for PDSCH transmission, where ν is the number of layers used forthe PDSCH transmission. UE-RSs are present and are a valid reference forPDSCH demodulation only if the PDSCH transmission is associated with thecorresponding antenna port. UE-RSs are transmitted only on RBs to whichthe corresponding PDSCH is mapped.

The UE-RSs are configured to be transmitted only on RB(s) to which aPDSCH is mapped in a subframe in which the PDSCH is scheduled unlikeCRSs configured to be transmitted in every subframe irrespective ofwhether the PDSCH is present. Accordingly, overhead of the RS maydecrease relative to overhead of the CRS.

In the 3GPP LTE-A system, the UE-RSs are defined in a PRB pair.Referring to FIG. 9, in a PRB having frequency-domain index nPRBassigned for PDSCH transmission with respect to p=7, p=8, or p=7, 8, . .. , ν+6, a part of UE-RS sequence r(m) is mapped to complex-valuedmodulation symbols.

UE-RSs are transmitted through antenna port(s) correspondingrespectively to layer(s) of a PDSCH. That is, the number of UE-RS portsis proportional to a transmission rank of the PDSCH. Meanwhile, if thenumber of layers is 1 or 2, 12 REs per RB pair are used for UE-RStransmission and, if the number of layers is greater than 2, 24 REs perRB pair are used for UE-RS transmission. In addition, locations of REsoccupied by UE-RSs (i.e. locations of UE-RS REs) in a RB pair are thesame with respect to a UE-RS port regardless of a UE or a cell.

As a result, the number of DM-RS REs in an RB to which a PDSCH for aspecific UE in a specific subframe is mapped is the same per UE-RSports. Notably, in RBs to which the PDSCH for different UEs in the samesubframe is allocated, the number of DM-RS REs included in the RBs maydiffer according to the number of transmitted layers.

The UE-RS can be used as the DM-RS in the embodiments of the presentdisclosure.

2.5 Enhanced PDCCH (EPDCCH)

In the 3GPP LTE/LTE-A system, Cross-Carrier Scheduling (CCS) in anaggregation status for a plurality of component carriers (CC: componentcarrier=(serving) cell) will be defined. One scheduled CC may previouslybe configured to be DL/UL scheduled from another one scheduling CC (thatis, to receive DL/UL grant PDCCH for a corresponding scheduled CC). Atthis time, the scheduling CC may basically perform DL/UL scheduling foritself. In other words, a search space (SS) for a PDCCH for schedulingscheduling/scheduled CCs which are in the CCS relation may exist in acontrol channel region of all the scheduling CCs.

Meanwhile, in the LTE system, FDD DL carrier or TDD DL subframes areconfigured to use first n (n<=4) OFDM symbols of each subframe fortransmission of physical channels for transmission of various kinds ofcontrol information, wherein examples of the physical channels include aPDCCH, a PHICH, and a PCFICH. At this time, the number of OFDM symbolsused for control channel transmission at each subframe may be deliveredto the UE dynamically through a physical channel such as PCFICH orsemi-statically through RRC signaling.

Meanwhile, in the LTE/LTE-A system, since a PDCCH which is a physicalchannel for DL/UL scheduling and transmitting various kinds of controlinformation has a limitation that it is transmitted through limited OFDMsymbols, enhanced PDCCH (i.e., E-PDCCH) multiplexed with a PDSCH morefreely in a way of FDM/TDM may be introduced instead of a controlchannel such as PDCCH, which is transmitted through OFDM symbol andseparated from PDSCH. FIG. 11 illustrates an example that legacy PDCCH,PDSCH and E-PDCCH, which are used in an LTE/LTE-A system, aremultiplexed.

3. LTE-U System

3.1 LTE-U System Configuration

Hereinafter, methods for transmitting and receiving data in a CAenvironment of an LTE-A band corresponding to a licensed band and anunlicensed band will be described. In the embodiments of the presentdisclosure, an LTE-U system means an LTE system that supports such a CAstatus of a licensed band and an unlicensed band. A WiFi band orBluetooth (BT) band may be used as the unlicensed band.

FIG. 12 illustrates an example of a CA environment supported in an LTE-Usystem.

Hereinafter, for convenience of description, it is assumed that a UE isconfigured to perform wireless communication in each of a licensed bandand an unlicensed band by using two CCs. The methods which will bedescribed hereinafter may be applied to even a case where three or moreCCs are configured for a UE.

In the embodiments of the present disclosure, it is assumed that acarrier of the licensed band may be a primary CC (PCC or PCell), and acarrier of the unlicensed band may be a secondary CC (SCC or SCell).However, the embodiments of the present disclosure may be applied toeven a case where a plurality of licensed bands and a plurality ofunlicensed bands are used in a carrier aggregation method. Also, themethods suggested in the present disclosure may be applied to even a3GPP LTE system and another system.

In FIG. 12, one eNB supports both a licensed band and an unlicensedband. That is, the UE may transmit and receive control information anddata through the PCC which is a licensed band, and may also transmit andreceive control information and data through the SCC which is anunlicensed band. However, the status shown in FIG. 12 is only example,and the embodiments of the present disclosure may be applied to even aCA environment that one UE accesses a plurality of eNBs.

For example, the UE may configure a macro eNB (M-eNB) and a PCell, andmay configure a small eNB (S-eNB) and an SCell. At this time, the macroeNB and the small eNB may be connected with each other through abackhaul network.

In the embodiments of the present disclosure, the unlicensed band may beoperated in a contention-based random access method. At this time, theeNB that supports the unlicensed band may perform a Carrier Sensing (CS)procedure prior to data transmission and reception. The CS proceduredetermines whether a corresponding band is reserved by another entity.

For example, the eNB of the SCell checks whether a current channel isbusy or idle. If it is determined that the corresponding band is idlestate, the eNB may transmit a scheduling grant to the UE to allocate aresource through (E)PDCCH of the PCell in case of a cross carrierscheduling mode and through PDCCH of the SCell in case of aself-scheduling mode, and may try data transmission and reception.

At this time, the eNB may configure a TxOP including N consecutivesubframes. In this case, a value of N and a use of the N subframes maypreviously be notified from the eNB to the UE through higher layersignaling through the PCell or through a physical control channel orphysical data channel.

3.2 Carrier Sensing (CS) Procedure

In embodiments of the present disclosure, a CS procedure may be called aClear Channel Assessment (CCA) procedure. In the CCA procedure, it maybe determined whether a channel is busy or idle based on a predeterminedCCA threshold or a CCA threshold configured by higher-layer signaling.For example, if energy higher than the CCA threshold is detected in anunlicensed band, SCell, it may be determined that the channel is busy oridle. If the channel is determined to be idle, an eNB may start signaltransmission in the SCell. This procedure may be referred to as LBT.

FIG. 13 is a view illustrating an exemplary Frame Based Equipment (FBE)operation as one of LBT operations.

The European Telecommunication Standards Institute (ETSI) regulation (EN301 893 V1.7.1) defines two LBT operations, Frame Based Equipment (FBE)and Load Based Equipment (LBE). In FBE, one fixed frame is comprised ofa channel occupancy time (e.g., 1 to 10 ms) being a time period duringwhich a communication node succeeding in channel access may continuetransmission, and an idle period being at least 5% of the channeloccupancy time, and CCA is defined as an operation for monitoring achannel during a CCA slot (at least 20 μs) at the end of the idleperiod.

A communication node periodically performs CCA on a per-fixed framebasis. If the channel is unoccupied, the communication node transmitsdata during the channel occupancy time. On the contrary, if the channelis occupied, the communication node defers the transmission and waitsuntil the CCA slot of the next period.

FIG. 14 is a block diagram illustrating the FBE operation.

Referring to FIG. 14, a communication node (i.e., eNB) managing an SCellperforms CCA during a CCA slot. If the channel is idle, thecommunication node performs data transmission (Tx). If the channel isbusy, the communication node waits for a time period calculated bysubtracting the CCA slot from a fixed frame period, and then resumesCCA.

The communication node transmits data during the channel occupancy time.Upon completion of the data transmission, the communication node waitsfor a time period calculated by subtracting the CCA slot from the idleperiod, and then resumes CCA. If the channel is idle but thecommunication node has no transmission data, the communication nodewaits for the time period calculated by subtracting the CCA slot fromthe fixed frame period, and then resumes CCA.

FIG. 15 is a view illustrating an exemplary LBE operation as one of theLBT operations.

Referring to FIG. 15(a), in LBE, the communication node first sets q(q∈{4, 5, . . . , 32}) and then performs CCA during one CCA slot.

FIG. 15(b) is a block diagram illustrating the LBE operation. The LBEoperation will be described with reference to FIG. 15(b).

The communication node may perform CCA during a CCA slot. If the channelis unoccupied in a first CCA slot, the communication node may transmitdata by securing a time period of up to (13/32)q ms.

On the contrary, if the channel is occupied in the first CCA slot, thecommunication node selects N (N∈{1, 2, . . . , q}) arbitrarily (i.e.,randomly) and stores the selected N value as an initial count. Then, thecommunication node senses a channel state on a CCA slot basis. Each timethe channel is unoccupied in one specific CCA slot, the communicationnode decrements the count by 1. If the count is 0, the communicationnode may transmit data by securing a time period of up to (13/32)q ms.

4. TxOP Configuration Method and Reservation Signal Transmission Method

A description will be given below of methods for transmitting areservation signal to occupy a channel and methods for configuring aTxOP, when the channel is determined to be idle after theabove-described CS (i.e., LBT) operation. In embodiments of the presentdisclosure, if it is said that ‘an SCell is determined to be idle’, thismeans that the SCell is determined to be idle during an LBT operation oris determined to be idle repeatedly as many times as a backoff countduring a backoff operation. In other words, an idle-state SCell meansthat upon completion of a CS procedure including a backoff operation oran LBT operation, the SCell is finally idle.

For the convenience of description, it is assumed that the size M of aTxOP is 3 (i.e., three subframes) in embodiments of the presentdisclosure. It is also assumed that a PCell operates in the LTE-A systemusing a licensed band and an SCell operates in an unlicensed band (e.g.,WiFi, BT, or the like). For details, refer to FIG. 12.

4.1 Methods for Configuring TxOP and Transmitting Reservation Signal inCase of Alignment with Subframe (SF) Boundary of PCell

Embodiments as set forth below are for a case in which an SCell isconfigured to operate in alignment with an SF boundary of a PCell.

FIGS. 16 and 17 are views illustrating a method for transmitting areservation signal.

FIGS. 16 and 17 illustrate a case in which an SCell is configured tooperate in alignment with an SF boundary of a PCell. If an eNB actuallytransmits data in the SCell in alignment with an SF boundary of theLTE-A system as illustrated in FIG. 16, there may exist a timing gapbetween a time of determining the idle state of the SCell and an actualdata transmission time. Particularly, since the SCell is defined in anunlicensed band, a specific eNB and a specific UE may use the SCell notexclusively but by CS-based contention. Therefore, another system (e.g.,a WiFi system) may attempt to transmit information during the timinggap.

Accordingly, to prevent another system from attempting informationtransmission during the timing gap of the SCell, the eNB may configuretransmission of a reservation signal. The reservation signal may be akind of “dummy information”, “a copy of a part of a PDSCH”, or “an RSsuch as CRS or DM-RS” that the eNB transmits to reserve the SCell as itsresources. The reservation signal may be transmitted during the timinggap (i.e., until before the actual data transmission time after the timeof determining the idle state of the SCell).

Referring to FIG. 16, the eNB may determine whether the SCell is in theidle state to transmit data in the SCell. That is, the eNB determineswhether the channel is idle by CS, and performs a backoff operation oran LBT operation according to the determination. If the eNB determinesthe SCell to be idle in SF #N and thus ends the backoff operation or theLBT operation, the eNB may transmit a reservation signal until beforethe next SF, SF #N+1, to thereby prevent another system from occupyingthe SCell.

However, if the eNB should transmit the reservation signal until thenext SF boundary after the time of determining the SCell to be idle inorder to align an SF boundary of the SCell with an SF boundary of thePCell, the eNB should transmit the reservation signal during almost oneSF period (i.e., 1 ms), as illustrated in FIG. 17. Referring to FIG. 17,if the eNB determines that the SCell is idle shortly after the start ofSF #N+1 after the backoff operation, the eNB should continuetransmitting the reservation signal in SF #N+1 in order to occupy theSCell in alignment between an SF boundary of the SCell and an SFboundary of the PCell.

If the transmission period of the reservation signal is too long asdescribed above, data transmission performance of the LTE/LTE-A systemmay be degraded, and the performance of a system (e.g., WiFi) operatingin an unlicensed band may also be degraded because the reservationsignal may act as interference.

4.1.1. Maximum Value Setting

To solve the above problem, a maximum value (i.e., X ms) of areservation signal transmission period may be preset. For example, themaximum value of the reservation signal transmission period may be setto one slot (i.e., 0.5 msec) or n OFDM symbols. X or n may be preset orset by higher layer signaling or physical layer signaling.

If the maximum value of the reservation signal transmission period isset to one slot, the eNB may start CS in the second slot of every SF,and transmit a reservation signal from a time of determining the SCellto be idle until the next SF of the PCell.

FIG. 18 is a view illustrating an embodiment of setting a maximum valuefor a reservation signal transmission period.

Referring to FIG. 18, if the eNB determines that a channel of the SCellis kept busy from the second slot of SF #N to the starting time of SF#N+1, the eNB may halt CS during one slot from the starting time of SF#N+1, and start to resume the CS in the second slot of SF #N+1.Subsequently, if the eNB determines the channel to be idle, the eNB maytransmit a reservation signal until before the starting time of the nextSF, SF #N+2, and start to transmit data in SF #N+2. If the size M of aTxOP is preset by higher layer signaling, a UE may receive data in theSCell during the TxOP.

4.1.2 Adjustment of Starting Time of SF in SCell

FIG. 19 is a view illustrating a method for adjusting the starting timeof an SF in an SCell according to an operation of a PCell.

As illustrated in FIG. 19(a), a time of determining the SCell to be idlemay be aligned with an SF boundary of the PCell. If at least Y ms isrequired to perform CCS in the PCell, it may be impossible to performCCS of the PCell in SF #N+1 of the SCell due to the processing delaytime of Y ms.

To solve the problem, an SF starting time of the SCell may be advancedby Y ms. For example, as SF #N+1 of the SCell is configured to start Yms earlier than SF #N+1 of the PCell as illustrated in FIG. 19(b), eventhough the channel is determined to be idle at a boundary of SF #N+1 ofthe SCell, the eNB may prepare for CCS for Y ms in the PCell.

Herein, Y may be predetermined in the system, or may be configuredsemi-statically by higher layer signaling or dynamically by physicallayer signaling (e.g., transmission of an (E)PDCCH) in each SF. Theinterval between SFs in the PCell and the SCell may be represented asthe number of OFDM symbols.

The eNB may be configured not to perform CS in the SCell during Y ms.

Or if the eNB determines the channel to be idle by CS during Y ms, theeNB may transmit the reservation signal during a timing gap untilshortly before the starting time of the next SF, SF #N+1 of the SCell(refer to FIG. 19(c)).

4.2 Method for Changing Size of First SF in TxOP

If the reservation signal is transmitted to align an SF boundary of theSCell with an SF boundary of the PCell as described in Section 4.1, lossmay occur in terms of spectral efficiency. To reduce the loss ofspectral efficiency, it may be configured that if a channel of the SCellis idle, data is transmitted in the SCell despite misalignment betweenthe SF boundary of the SCell and the SF boundary of the PCell.

For example, data transmission efficiency may be increased byconfiguring the first SF of a TxOP in the SCell in such a manner thatthe length of the first SF may be changed. Additionally, the reservationsignal may be configured to be transmitted to align an SF boundary ofthe SCell with a slot boundary of the PCell. Now, a description will begiven of methods for configuring a TxOP in an SCell in alignment with aslot boundary of a PCell.

FIG. 20 is a view illustrating a method for aligning an SF boundary ofan SCell with a slot boundary of a PCell.

It may be configured that data transmission (i.e. a TxOP) of the SCellstarts at a slot boundary of the PCell. For example, referring to FIG.20, if determining a channel of the SCell to be idle in the first slotof SF #N+1, the eNB may transmit the reservation signal only until theboundary of the second slot of SF #N+1. Herein, since a boundary of theSCell may be aligned with a slot boundary of the PCell, the TxOP of theSCell may start in the second slot of SF #N+1. That is, the first SF ofthe TxOP can be not a full SF but a partial SF (pSF) including only oneslot. The eNB may transmit data in the first SF of the SCell alignedwith a slot boundary of SF #N+1 of the PCell. Each of the remaining SFsof the TxOP is of the same length as an SF of the PCell, and the end ofthe last SF of the TxOP may be aligned with the end of SF #N+3 in thePCell.

In another aspect of the embodiment, a time point (i.e., the startingtime of a TxOP) at which data transmission may start in the SCell may beset to a symbol boundary of the PCell, not a slot boundary of the PCell.Or the start of the TxOP in the SCell may be set only to a specific timepoint of the PCell. For example, the TxOP of the SCell may start at theboundary of an odd-numbered or even-numbered symbol of the PCell.

In embodiments of the present disclosure, the first SF of the TxOP inthe SCell may be configured to be a pSF shorter than a legacy SF of 1ms. Therefore, methods for determining a Transport Block Size (TBS) forthe first SF of a TxOP and methods for transmitting an RS in the firstSF of the TxOP will be described below.

4.2.1 TBS Determination Method-1

According to the LTE/LTE-A system standard TS 36.213, 7.1.7, a TBS isdetermined according to a 5-bit Modulation and Coding Scheme (MCS) field(i.e., I_(MCS)) included in DCI and the number of Physical ResourceBlocks (PRBs), N_(PRB). N_(PRB) is determined in the manner described in[Table 6].

TABLE 6 <TS 36.213 7.1.7> ...  - set N_(PRB)′ to the total number ofallocated PRBs based on the procedure defined in subclause 7.1.6.    ifthe transport block is transmitted in DwPTS of the special    subframein frame structure type 2, then    ∘ for special subframe configuration9 with normal cyclic prefix or special subframe configuration 7 withextended cyclic prefix: ▪ set the Table 7.1.7.2.1-1 column indicatorN_(PRB) = max {└N_(PRB)′ ×0.375┘, 1}    ∘ for other special subframeconfigurations: ▪ set the Table 7.1.7.2.1-1 column indicator N_(PRB) =max {└N_(PRB)′ ×0.75┘, 1}, else, set the Table 7.1.7.2.1-1 columnindicator N_(PRB) = N_(PRB)′ .

If the first SF of a TxOP in an SCell is a pSF, a TBS may be determinedas follows. When one SF is divided into T points and the first SF startsat a k^(th) point among the T points, N_(PRB) for the pSF may becalculated by the following [Equation 3].

$\begin{matrix}{N_{PRB} = {\max\left\{ {\left\lfloor {N_{PRB}^{\prime} \times \frac{k}{T}} \right\rfloor,1} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

For example, if a normal CP is used in the SCell and the SCell operatesin alignment with a symbol boundary of a PCell, T may be set to 14 and kmay represent the index of an OFDM symbol in the first SF. Herein, k maybe indicated by DCI on a PDCCH transmitted in SF #N+2.

Or if an extended CP is used in the SCell and the SCell operates inalignment with a symbol boundary of the PCell, T may be set to 12 and kmay represent the index of an OFDM symbol in the first SF.

4.2.2 TBS Determination Method-2

Among the methods proposed in Section 4.2.1, an SF including as manyOFDM symbols as defined by a legacy DwPTS configuration will bedescribed. That is, if the first SF of a TxOP is configured as in aDwPTS configuration described in [Table 1], N_(PRB) may be calculated.

For example, if the first SF includes 7 OFDM symbols, N_(PRB) may becalculated by N_(PRB)=max {└N′_(PRB)×0.375┘, 1} like special SFconfiguration 9 in [Table 1]. If the first SF includes 9 to 12 OFDMsymbols, N_(PRB) may be calculated by N_(PRB)=max {└N′_(PRB)×0.75┘, 1}like special SF configurations 1, 2, 3, 4, 6, 7 and 8. The same thing isapplicable to an extended CP case.

4.2.3 RS Configuration Method-1

FIG. 21 is a view illustrating configurations of RSs transmitted in anSCell.

In the LTE/LTE-A system, the eNB transmits DM-RSs configured asillustrated in FIG. 21(a) to help a UE with data demodulation. However,if the first SF of a TxOP in an SCell is configured to be shorter thanthe length of the legacy SF, 1 ms, DM-RSs sufficient for datademodulation may not be ensured.

For example, if the length of the first SF is equal to or smaller thanQ, DM-RSs may be transmitted in the pattern illustrated in FIG. 21(b). Qmay be configured semi-statically by higher layer signaling ordynamically by physical layer signaling. For example, Q may be definedto be one slot. That is, if the first SF includes only one slot, DM-RSsallocated to the first SF may be configured as illustrated in FIG.21(b).

The reason for configuring DM-RSs in the pattern illustrated in FIG.21(b) is that since the former boundary of the first SF may varyaccording to a channel state-based CS result, sufficient DM-RSs may notbe ensured. Therefore, DM-RSs are preferably allocated to the secondslot.

4.2.4 Setting of SF Length Based on Threshold

If an SCell operates in alignment with a symbol boundary of a PCell, thefirst SF of a TxOP may include only one OFDM symbol in an extreme case.

However, it may be more efficient in terms of SCell management toconfigure an SF having a long TTI by concatenating one SF with anotherSF than to configure an independent SF with too small a number of OFDMsymbols. That is, it may be determined whether to configure an SF byconcatenating the first SF with another SF based on a specificthreshold.

The threshold may be a predetermined fixed value in the system, or maybe configured semi-statically by higher layer signaling or dynamicallyby physical layer signaling. For example, the threshold may be set asthe number of OFDM symbols.

FIG. 22 is a view illustrating a method for determining an SF lengthbased on a threshold.

If the first SF includes as many OFDM symbols as or fewer OFDM symbolsthan a threshold, the first SF may be concatenated with the next SF intoone SF. Referring to FIG. 22, it may be noted that a TxOP starts in alatter part of SF #N+1 in a first SCell. That is, if the length of theTxOP in SF #N+1 with respect to an SF boundary of a PCell is equal to orsmaller than a threshold, the TxOP of SF #N+1 and the TxOP of SF #N+2 inthe SCell may be concatenated into the first SF.

Or if the first SF includes more OFDM symbols than the threshold, thefirst SF may be configured to be independent of the next SF. Referringto FIG. 22, it may be noted that a TxOP starts in a former part of SF#N+1 in a second SCell. That is, if the length of the TxOP in SF #N+1with respect to an SF boundary of the PCell is larger than thethreshold, the first SF of the TxOP of SF #N+1 may be configured to beindependent of the TxOP of SF #N+2.

That is, if the SCell is determined to be idle in SF #N+1, the first SFof the TxOP may be configured to be an independent pSF, or an over SF(oSF) produced by concatenating the SF with the next SF, depending onwhether the number of OFDM symbols in the TxOP is equal to or largerthan the threshold.

In another aspect of the embodiment, as is the case with a special SFconfiguration that does not allow PDSCH transmission (i.e., special SFconfigurations 0 and 5 in a normal CP case, and special SFconfigurations 0 and 4 in an extended CP case) in the current LTE/LTE-Asystem, the first SF may be configured with three or fewer OFDM symbols.In this case, the first SF may be concatenated with the next SF into oneSF.

4.2.5 TBS Determination Method-3

When the first SF is configured with more OFDM symbols than a thresholdin Section 4.2.4, a TBS may be calculated in the methods described inSection 4.2.1 and Section 4.2.2. However, if the first SF is configuredto be an oSF by concatenating as many OFDM symbols as or fewer OFDMsymbols than the threshold with the next SF, N_(PRB) may be determinedby the following [Equation 4].

$\begin{matrix}{N_{PRB} = {\max\left\{ {\left\lfloor {N_{PRB}^{\prime} \times \frac{T + k}{T}} \right\rfloor,1} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In [Equation 4], k or (T+k) may be transmitted to a UE in DCI of SF #N+2by CCS.

However, if a normal CP is used, the threshold is 3 OFDM symbols, and kis 3, N_(PRB) is calculated by N_(PRB)=max {└N′_(PRB)×17/14┘, 1} whereif N′_(PRB)=100, N_(PRB)=121 larger than a maximum value of N_(PRB) asdefined in the current LTE/LTE-A system. To prevent this, N_(PRB) may bedetermined by [Equation 5].

$\begin{matrix}{N_{PRB} = {\min\left\{ {{\max\left\{ {\left\lfloor {N_{PRB}^{\prime} \times \frac{T + k}{T}} \right\rfloor,1} \right\}},Z} \right\}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In [Equation 5], Z is a maximum available number of PRBs in a systemBandWidth (BW) given to the SCell. For example, Z may be set to 110.

If N_(PRB) calculated by [Equation 4] is larger than Z, N_(PRB) may becalculated in the following manner, instead of the method described by[Equation 5]. For example, if a TBS determined by I_(TBS) and N_(PRB)(refer to the LTE standard TS 36.213, Table 7.1.7.2.1-1) is defined asTBS(I_(TBS), N_(PRB)), an actual TBS may be calculated by [Equation 6].

$\begin{matrix}{{{TBS}\left( {I_{TBS},N_{PRB}} \right)} = \left\lfloor {{{TBS}\left( {I_{TBS},N_{PRB}^{\prime}} \right)} \times \frac{T + k}{T}} \right\rfloor} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In another aspect of the embodiment, the UE may be configured not toexpect N_(PRB) calculated by [Equation 4] larger than Z. That is, the UEmay ignore or discard DCI that configures N_(PRB) larger than Z.

4.2.6 RS Configuration Method-2

When one SF is configured by concatenating the first SF of a TxOP withthe next SF in Section 4.2.4, CRSs may be transmitted not in OFDMsymbols concatenated to the next SF, but in the full OFDM symbols of thenext SF. The UE may perform channel estimation using the CRSs.

Or, DM-RSs may not be transmitted in the OFDM symbols concatenated tothe next SF, and the UE may perform data demodulation using DM-RSs inthe next full SF.

For example, referring to FIG. 22, CRSs and/or DM-RSs are allocated notto OFDM symbols corresponding to SF #N+1 in the first SF of the TxOP,but to an area corresponding to SF #N+2.

In another aspect of the embodiment, the UE may configure CRSs and/orDM-RSs for the OFDM symbols concatenated to the next SF by copying apart (e.g., a former or latter part) of the following full SF.

4.3 Method for Fixing Length of First SF in TxOP

If a reservation signal and data are transmitted in an SCell in themethods described in Section 4.2, an eNB managing a PCell does not knowat the starting time of SF #N+1 when data transmission actually startsin the SCell. Accordingly, the eNB preferably determines a TBS and anMCS for each available SF configuration unit in advance, and preparesfor data transmission suitable for each unit.

If data transmission is possible at an OFDM symbol boundary, a total of14 lengths ranging from 1 OFDM symbol to 14 OFDM symbols are availableas the length of the first SF of a TxOP. Therefore, at the start of SN#N+1, the eNB should prepare 14 different data having different TBSs andMCSs for 14 starting points, thereby increasing the configuration andscheduling complexity of the SCell.

Now, a description will be given of a transmission method for reducingcomplexity in relation to an SCell, and a related TBS determinationmethod and RS transmission method.

In Section 4.2, the TBS of the first SF of a TxOP in an SCell isadjusted for alignment with an SF boundary of a PCell, starting from SF#N+2. In contrast, an embodiment of the present disclosure as describedbelow is about methods for reducing the complexity of an SCell by fixingthe length of the first SF of a TxOP in the SCell to the length (e.g., 1ms) of an SF in a PCell.

For example, if it is possible to transmit data in the SCell inalignment with a slot boundary of the PCell, even though transmission ofthe first SF starts in an odd-numbered slot of the PCell, an SF may beconfigured to be as long as the legacy SF and the last SF of the TxOPmay be transmitted during one slot (i.e., 0.5 ms).

As a consequence, there is no need for preconfiguring the first SF in aplurality of units in the PCell at the starting time of SF #N+1, and thelast SF of the TxOP has only to be configured in a variable length,thereby reducing the complexity of the SCell.

FIG. 23 is a view illustrating a method for fixing the length of thefirst SF of a TxOP.

Referring to FIG. 23, an SCell is determined to be idle in SF #N+1, anda TxOP is allocated, starting from SF #N+1. The last SF (i.e., the thirdSF) of the TxOP may be configured to be in a variable length, foralignment with an SF boundary of a PCell.

If the last SF of the TxOP is aligned with a boundary of the PCell, aprocessing delay may be reduced on the part of the eNB, if SF #N+4 isconfigured as a UL SF. For example, UL transmission may be performedimmediately in SF #N+4. In addition, in the case of a non-TDDconfiguration, the freedom of DL/UL configuration may be increased.

4.3.1 TBS Determination Method-4

Since the first SF of a TxOP is configured to be of the same length asan SF in a PCell, a TBS may be set to be equal to that of the PCell.However, considering that the last SF of the TxOP has a variable length,the eNB may configure a TBS using the TBS determination method describedin Section 4.2.1 and/or Section 4.2.2, and the UE may receive and decodedata by determining a TBS based on DCI received from the eNB.

4.3.2 Special SF Configuration

The last SF of a TxOP may be configured to include only as many OFDMsymbols as defined in a DwPTS configuration being a specific SFconfiguration (refer to [Table 1]).

Or, it may be restricted that the SF should be configured only withunits of a specific OFDM symbol (e.g., an even number of OFDM symbols).In this case, the actual length of the last SF may not match a regulatedtransmission unit for the last SF. For example, although it is regulatedthat the last SF is transmitted only in units of a slot, the actualnumber of OFDM symbols in the last SF may be only 3. In this case, itmay be defined that the last SF is not configured.

That is, the last SF may be configured with the largest of definedtransmission units for the last SF, shorter than the actual length ofthe last SF. For example, if the last SF is configured with as many OFDMsymbols as defined by a legacy DwPTS configuration, the unit of the lastSF defined for the case of a normal CP is 3, 7, 9, 10, 11, 12, or 14OFDM symbols. If the actual length of the last SF is 13 OFDM symbols,the last SF may be configured only with 12 OFDM symbols. That is, thelast SF may be configured with the largest of SF units smaller than adefined size.

4.3.3 DM-RS Configuration Method

Similarly to the description of Section 4.2.3, if the last SF isconfigured to be shorter than the SF length (i.e., 1 ms) of a PCell, forexample, if the last SF is configured with only one slot, DM-RSs enoughfor data demodulation may not be ensured.

To avert the problem, if the length of the last SF is smaller than Q, itmay be configured that DM-RSs are transmitted in the pattern illustratedin FIG. 24. FIG. 24 is a view illustrating a method for allocatingDM-RSs, when the last SF of a TxOP is configured variably.

The DM-RS configuration method illustrated in FIG. 24 is applied for aspecial SF configuration. For example, Q may be set to one slot. Q maybe configured for the UE by higher layer signaling or physical layersignaling.

4.3.4 Method for Configuring Last SF Based on Threshold

If an SCell operates in alignment with a symbol boundary of a PCell asdescribed in Section 4.2.4, the last SF of a TxOP may be configured onlywith one OFDM symbol in an extreme case. FIG. 25 is a view illustratinga case of fixing the length of the first SF of a TxOP. Referring to FIG.25, it may be noted that when the size M of a TxOP is 3, the length ofthe last third SF of the TxOP is one OFDM symbol.

Also in this case, an SF may be configured and a TBS may be determinedin the methods described in Section 4.2.4 and Section 4.2.5. Forexample, the last third SF and the previous second SF may beconcatenated into one SF.

However, if the last SF is configured to be longer than the legacy SFlength, the resulting decoding delay may affect an HARQ-ACK process.Therefore, it may not be reasonable to set the length of the last SF tobe larger than the legacy SF length. In this context, the length of thefirst SF may be set variably, rather than the last SF is set to belonger than the legacy SF length. As a consequence, the length of thelast SF may not be smaller than a specific value.

FIG. 26 is a view illustrating one of methods for configuring the firstand last SFs of a TxOP based on a threshold.

Referring to FIG. 26, a slot boundary of a PCell is set as a threshold.In the case where an SCell is determined to be idle in SF #N+1, if thefirst SF of a TxOP starts before the threshold, the length of the firstSF may be set to the legacy SF length. If the first SF of the TxOPstarts after the threshold, the length of the first SF may be set to oneslot.

This configuration may always maintain the length of the last SF to belarger than one slot. In FIG. 26, the first SF of a TxOP starts before athreshold in a first SCell and thus is configured to be 1 ms long. Thelast SF of the TxOP may be configured to be 1 ms-a (a=<0.5 ms) long.

In a second SCell, the first SF of a TxOP starts after the threshold.Thus, the first SF may be configured to include one slot (i.e., 0.5 ms).The second SF of the TxOP may be 1 ms long as in a PCell, and a lengthequal to or larger than 0.5 ms may be ensured for the third SF of theTxOP because the first SF is 0.5 ms long. That is, the length of thelast SF may be set to 0.5 ms+a (a=<0.5 ms).

The threshold may be allocated semi-statically by higher layer signalingor dynamically by physical layer signaling. The TBSs of the first SF andthe last SF may also be determined in the method described in Section4.2.1, Section 4.2.2, and/or Section 4.3.2.

DM-RSs may be determined for the first SF and the last SF in the methodproposed in Section 4.2.3.

In the afore-described Section 4.3.1 to Section 4.3.3, the eNB mayindicate the number of OFDM symbols in the last SF to the UE in SF #N+4in the PCell by CCS. Or each UE may calculate the number of OFDM symbolsin the last SF of the TxOP based on the starting time of the first SFand the threshold in the above-described rule.

4.4 TxOP Configuration Method-1

4.4.1 Method for Determining Starting Time of TxOP Based on Threshold

As described regarding the transmission starting time of data in anSCell from an eNB in Section 4.1, data may be transmitted by aligning anSF boundary of the SCell with an SF boundary of a PCell. Or data may betransmitted in alignment with a slot boundary or OFDM symbol boundary ofthe PCell instead of an SF boundary of the PCell, as described before inSection 4.2 and/or Section 4.3.

Now, a description will be given of a method for transmitting areservation signal based on a threshold, and a method for determining astarting time of data transmission.

FIG. 27 is a view illustrating another of the methods for transmitting areservation signal based on a threshold.

In FIG. 27, it is assumed that a PCell and an SCell are configured asdescribed before with reference to FIG. 12. A threshold for transmittinga reservation signal and/or determining a starting time of datatransmission may be a predetermined fixed value in the system, or may beallocated semi-statically by higher layer signaling or dynamically byphysical layer signaling.

The threshold may be defined as t μs after (or before) an SF boundary ofthe PCell, or as an m^(th) OFDM symbol boundary. If a backoff operationor a CS operation is completed earlier than the threshold, the eNB mayconfigure an SF in a unit shorter than one SF (i.e., 1 ms) and startdata transmission in the configured SF, after transmitting a reservationsignal in the SCell (or without transmitting the reservation signal).

It may be configured that actual data transmission starts at thethreshold (refer to SCell 3 in FIG. 27) or at a predetermined time point(e.g., an OFDM symbol boundary) earlier than the threshold (refer toSCell 2 in FIG. 27). On the other hand, if the backoff operation or theCS operation is completed after the threshold, a reservation signal maybe transmitted until the next SF boundary, and then data transmissionmay start (refer to SCell 1 in FIG. 27).

Referring to FIG. 27 again, if the eNB is to transmit data in an SCellof an unlicensed band, the eNB performs a backoff operation and a CSoperation in the SCell. If determining that the SCell is idle in SF#N+1, the eNB may configure a TxOP and transmit data in the TxOP.

Notably, the eNB may align a data transmission time (i.e., the startingtime of the first SF of the TxOP) with an SF boundary, OFDM symbolboundary, or slot boundary of the PCell. While it is assumed that thethreshold is set as a slot boundary in FIG. 27, the threshold may varyaccording to a channel environment.

In SCell 1, since the eNB has completed the backoff operation and the CSoperation at a time point after the threshold, the eNB may align thestarting time of the first SF of the TxOP with a boundary of SF #N+2 inthe PCell.

In SCell 2, since the eNB has completed the backoff operation and the CSoperation at a time point before the threshold, the eNB may align thestarting time of the first SF of the TxOP with a slot boundary or OFDMsymbol boundary of the PCell. It is assumed that the starting time ofthe first SF is aligned with a slot boundary of the PCell in SCell 2.

In SCell 3, since the eNB has completed the backoff operation and the CSoperation at the threshold, the eNB may align the starting time of thefirst SF of the TxOP with a slot boundary or OFDM symbol boundary of thePCell. It is assumed that the starting time of the first SF is alignedwith a slot boundary of the PCell in SCell 3.

Or if the backoff operation or the CS operation is completed after thethreshold, the eNB may perform the backoff operation or the CS operationagain without transmitting a reservation signal in the SCell, start datatransmission at the next SF boundary without transmitting thereservation signal, or perform the backoff operation or the CSoperation, starting at the next SF boundary without transmitting thereservation signal.

4.4.2 Method for Setting Starting Time of TxOP Based on Code Rate

A method for determining the starting time of a TxOP using a time-axisthreshold has been described above in Section 4.4.1. Now, a descriptionwill be given of methods for determining the starting time of a TxOPbased on a code rate.

For example, a threshold Y may be set for a code rate. If an SF may beconfigured to be a smaller unit than one 1-ms SF unit, the eNB may startdata transmission only when a code rate is equal to or lower than Y.This is because if data is transmitted at a code rate higher than Y, itmay occur that the eNB may not ensure the reliability of transmissiondata.

Or the eNB may transmit only data corresponding to a maximum TBS with acode rate equal to or lower than Y. As described before in Section4.4.1, the eNB may transmit a reservation signal between an ending timeof a CS or backoff operation and a data transmission time.

If the code rate is higher than the threshold Y, the eNB may transmit areservation signal until the next SF boundary, perform the CS operationagain, starting from the next SF boundary, while giving up datatransmission, or perform data transmission.

The threshold Y may be preset in the system or configured by physicallayer signaling or higher layer signaling.

If an SF shorter than 1 ms is configured in Section 4.4.1 or Section4.4.2, a TBS may be determined according to the method proposed inSection 4.2.1 or Section 4.2.2. Or a code rate may be determinedaccording to a puncturing or rate matching method after a TBS isdetermined in Section 4.4.1 or Section 4.4.2.

4.4.3 HARQ Process Configuration

If the first SF of a TxOP is configured with as many OFDM symbols as orfewer OFDM symbols than a threshold, the OFDM symbols and the next SFmay be concatenated into one SF, as described in Section 4.2.4. Or ifthe first SF is configured with more OFDM symbols than the threshold,the OFDM symbols may be configured as an independent SF.

Now, an HARQ-ACK configuration will be proposed. If the first SF isconfigured by concatenating as many OFDM symbols as or fewer OFDMsymbols than a threshold to the next SF, the UE may regard the first SFas one HARQ process. On the other hand, if the first SF is configuredwith more OFDM symbols than the threshold, the UE may consider that anHARQ process has been configured for each independent SF. That is, theUE may consider that separate (i.e., two) HARQ processes have beenconfigured for the first SF of a length shorter than 1 ms but largerthan the threshold and the next second SF.

In another aspect of the embodiment, if the first SF is configured to beshorter than 1 ms, an HARQ-ACK for the first SF may be bundled with anHARQ-ACK for the next SF (or the previous SF), that is, a full 1-ms SF.

4.4.4 Special SF Configuration

If a short SF which is not defined in the DwPTS configurations describedin Section 3 is configured and transmitted, the eNB may not give up datatransmission in the SF and transmit only data without allocating RSssuch as CRSs or DM-RSs.

4.5 TxOP Configuration Method

4.5.1 Method for Configuring TxOP in Case of Aligning SF Boundary ofSCell with SF Boundary of PCell

When an SCell is determined to be idle, the starting time of datatransmission may be aligned with an SF boundary of a PCell, as describedin Section 4.1.2 with reference to FIG. 19. The eNB may require at leastY1 ms as a processing time for DCI configuration in performing CCS inthe PCell (or the SCell).

FIG. 28 is a view illustrating a method for transmitting a reservationsignal.

Hereinbelow, a method for ensuing Y1 ms (or an Y2 OFDM symbol time) forconfiguring DCI while an SF boundary of an SCell is aligned with an SFboundary of a PCell as described in Section 4.1.2 and the alignment ismaintained (e.g., within a time error of 30.26 μs in the LTE-A system)is proposed.

In FIG. 28, only when a backoff operation is completed Y1 ms earlierthan the starting time of SF #N+1 or a condition for stating datatransmission in a TxOP is satisfied as in SCell 1 or SCell 2, the eNBmay start data transmission in SF #N+1.

For example, if the eNB performs CCA only during Tμs without backoff asin SCell 3 in FIG. 28, the eNB may perform CCA during T μs Y1 ms beforeeach SF boundary.

If the SCell is determined to be idle in a CCA period of SF #N, the eNBmay transmit a reservation signal during Y1 ms and start datatransmission in SF #N+1. If the SCell is busy, the eNB may determineagain whether the SCell is busy or idle in a CCA period of SN #N+1. IfY1 ms is shorter than two OFDM symbols, the reservation signal may beconfigured to include DM-RSs.

In another aspect of the embodiment, the eNB may transmit a reservationsignal during Y1 ms to align a boundary of the SCell with an SF boundaryof the PCell.

4.5.2 Method for Configuring TxOP in Case of Alignment with SlotBoundary of PCell

Methods for ending a TxOP at an SF boundary have been described inSection 4.2 with reference to FIG. 20. However, the eNB may not end theTxOP at an SF boundary to match a total time during which the TxOP isconfigured (i.e., M=3 SFs). If a maximum length of consecutivetransmissions in an unlicensed band is limited (e.g., to 4 ms) and theTxOP ends at an SF boundary, short of the maximum length, radioresources may be inefficiently utilized.

If the last SF of the TxOP is a pSF shorter than 1 ms, the TBSdetermination methods and the RS transmission methods described inSection 4.2.1 to Section 4.2.4 are applicable to the pSF.

If the starting time of a TxOP is set to a point other than an SFboundary according to the ending time of CS (i.e., CCA) (e.g., on a slotbasis or an OFDM symbol basis (one of the starting times of 14 OFDMsymbols) as in the proposed methods of Section 4.2 and Section 4.3, thatis, if the length of the first SF of the TxOP is allowed to be variablein every TxOP, signaling of an RS configuration for the first SF and atransmission length of the first SF may become complex, which may makeactual UE implementation difficult.

On the other hand, in embodiments in which an eNB transmits data byaligning the start and end of a TxOP in an SCell with SF boundaries of aPCell, if a specific eNB is to configure consecutive TxOPs, one SF mayalways be wasted for performing CCA and transmitting a reservationsignal between TxOPs.

FIG. 30 is a view illustrating one of methods for configuringconsecutive TxOPs.

FIG. 30(a) illustrates a method for configuring consecutive TxOPs, whena boundary of an SCell is aligned with an SF boundary of a PCell asdescribed in Section 4.1. Referring to FIG. 30(a), when an eNB ends thefirst TxOP in SF #N−1 and then immediately wants to start the next TxOP,the eNB should wait until the next SF boundary even though CCS iscompleted in the middle of SF #N.

That is, the eNB should transmit a reservation signal instead of datafrom the ending time of CCA to the starting time of SF #N+1. Ashortcoming with this scheme is that if the length of a TxOP for datatransmission is set to up to 3 ms, the resources of one SF out of fourSFs may not be used for data transmission, if consecutive TxOPs are tobe configured.

To solve the problem, a TxOP configuration illustrated in FIG. 30(b) maybe considered. Referring to FIG. 30(b), the eNB may configure the endingtime of the last SF of a TxOP to be earlier than an SF boundary of aPCell, and perform CCA during a timing gap lasting until the next SFboundary. If the CCA operation (e.g., initial CCA and/or ECCA) iscompleted during the timing gap, the eNB may configure a TxOP to startat the next SF boundary.

If there is a TxOP ending in SF #N−1, the eNB may end the TxOP before anSF boundary at which SF #N starts, to perform a backoff operation and/ora CCA operation for configuring the next TxOP. If the CCA operation endsbetween the ending time of the TxOP and the starting time of SF #N, theeNB may transmit a reservation signal until before the starting time ofSF #N, and then immediately configure a TxOP at the starting time of SF#N.

Compared to the TxOP configuration illustrated in FIG. 30(a), the TxOPconfiguration illustrated in FIG. 30(b) offers the benefit of a greatdecrease in a non-data transmission period between TxOPs. The SFstructure illustrated in FIG. 30(b) is characterized in that the lengthof the last SF of a TxOP (or the last SF of a TxOP having a maximumavailable length) may be determined fixedly or semi-statically. The lastSF may be shorter than a 1-ms full SF. That is, the last SF may beconfigured to be a pSF, and the TBS determination methods and the RStransmission methods described in Section 4.3.1 to Section 4.3.4 areapplicable to the pSF.

While a timing gap is positioned in the last SF of each TxOP toconfigure consecutive TxOPs without SF waste in the TxOP configurationillustrated in FIG. 30(b), the timing gap may be positioned in the firstSF of each TxOP as illustrated in FIG. 30(c).

In FIG. 30(c), the length of the first SF of a TxOP may be determinedfixedly or semi-statically. For example, the first SF may be shorterthan a 1-ms full SF. That is, the first SF may be configured to be apSF, and the TBS determination methods and the RS transmission methodsdescribed in Section 4.2.1 to Section 4.2.6 are applicable to the pSF.

In another aspect of the embodiment, the methods proposed in FIG. 30 maybe easily extended to an LBT method in which if a channel is determinedto be idle at a predetermined time point after CCA, a TxOP startsimmediately without transmission of a reservation signal.

4.6 TBS Configuration Method-5

The eNB preferably prepares different TBSs according to pSF lengths forthe case of transmission of a pSF shorter than the legacy SF length, 1ms, as in SF #N+1 in FIG. 20 described in Section 4.2. That is, the eNBmanaging a PCell or an SCell does not know at the starting time of SF#N+1 when data transmission will start in the SCell.

Accordingly, the eNB should determine a TBS and an MCS for eachavailable pSF configuration unit in advance, and prepare for datatransmission suitable for each unit. If data transmission is possible atan OFDM symbol boundary, a total of 14 lengths ranging from 1 OFDMsymbol to 14 OFDM symbols are available as the length of the first SF ina TxOP. Therefore, at the starting time of SN #N+1, the eNB shouldprepare 14 different data having different TBSs and MCSs for 14 startingpoints, thereby increasing the configuration complexity of the SCell.

A description will be given below of a method for allocating a fixed TBSto a pSF, even though the pSF shorter than the legacy SF length (e.g., 1ms) is configured, in order to avert the above problem.

4.6.1 Change of Received RB Size of PDSCH According to Variable SFLength

For example, in the case where 5 RBs are scheduled on the assumption of10 symbols (10×5), if an SF length is 5 symbols, the UE may receive asignal by extending the RBs to 10 RBs for 5 symbols (5×10).

On the contrary, in the case where 10 RBs are scheduled on theassumption of 5 symbols, if an SF length is 10 symbols, the UE mayreceive a signal only in 5 RBs out of allocated 10 RBs.

Because the total number of RBs available in the system is limited, aPDSCH may not be transmitted to some UE. In this case, buffer handlingfor the UE failing in PDSCH reception may be performed using an NDI orthe like. Considering this UE operation, only initial transmission maybe allowed in a pSF.

4.6.2 TBS Based on Minimum SF Length and Assumption of Repetition of theTBS

For example, a TBS may be determined on the assumption that a minimum SFlength is 3 symbols. If an SF length is determined to be 6 symbols, theeNB may transmit the same TB twice. However, a repetition number may notnecessarily be limited to an integer multiple. For example, if 5 symbolsare secured, a TB may be configured to be repeated (1+⅔) times.

Redundancy versions may be cyclically applied to the repeated TBs in apredefined pattern (e.g., 0→2→3→1). As the eNB transmits the same TBrepeatedly, a data throughput is reduced but robust transmission ispossible. Therefore, a retransmission number may be reduced.

4.7 Method for Restricting Starting Time of TxOP

To increase the efficiency of radio resource utilization in the LTEsystem operating in an unlicensed band as illustrated in FIG. 20 asdescribed in Section 4.2, a TxOP for data transmission may start at atime point other than an SF boundary.

However, if a TxOP is allowed to start in each OFDM symbol, theimplementation complexity of an eNB and a UE may be increased. This isbecause the eNB should prepare a plurality of sets of TBS and REmappings in advance and the complexity of detecting the starting time ofa TxOP may be increased in the UE.

Therefore, in another embodiment of the present disclosure, the startingtime of a TxOP may be confined to a specific OFDM symbol. The followingdescription is given on the assumption that the starting time of a TxOPis limited to the first or fourth OFDM symbol (i.e., a part of OFDMsymbols with CRS port 0) of an SF. However, this constraint may beextended to a slot unit (e.g., a boundary of the first or second slot).

In general, the eNB determines a TBS at least hundreds of μsec earlierin order to transmit data in SF #N, and indicates the determined TBS byhigher layer signaling to transmit data corresponding to the TBS. If aTxOP starts at an SF boundary of the PCell, the eNB may transmit data in14 OFDM symbols. Or if the TxOP starts in the fourth OFDM symbol, theeNB may transmit data in 10 OFDM symbols.

Although the eNB may not predict the starting time of a TxOPpreliminarily hundreds of μs earlier during an LBT operation, if the eNBprepares for TBSs and so on for two starting time points, eNBimplementation complexity may be increased significantly.

To solve the problem, the eNB may prepare only one TB S irrespective ofthe starting time of the first SF of a TxOP. A method for scaling a PRBsize in determining a TBS for transmission in 10 OFDM symbols may bedetermined according to Section 4.2.1 or Section 4.2.2.

If the UE receives an SF including a partial TTI (i.e., a pSF), the UEmay determine a TBS based on the number of transmission OFDM symbols andthe number of OFDM symbols preset independently between the eNB and theUE.

From the perspective of the eNB, the eNB may assume a full SF (i.e., 14OFDM symbols) in pSF transmission or assume that a pSF is configuredwith fewer OFDM symbols than a predetermined number of OFDM symbols,that is, 14 OFDM symbols.

If it is regulated that when the eNB transmits a pSF, the eNB assumestransmission of a full SF all the time, the UE may decode the pSF on theassumption of receiving a full SF.

Further, if it is regulated that when the eNB transmits a pSF, the eNBassumes transmission of a predetermined smaller number of OFDM symbols,the UE may decode the pSF on the assumption of receiving an SF includingthe predetermined smaller number of OFDM symbols.

In this case, as the eNB configures an SF configuration unit for the UEwhen transmitting the pSF, the UE may decode the pSF based on theconfigured SF configuration unit.

Now, a description will be given below of methods for determining a TBSfor a configured pSF according to this rule.

4.7.1 TBS Configuration in Predetermined Rule

The eNB may configure an SF with a fixed number of OFDM symbols (e.g.,10 OFDM symbols) as the first SF of a TxOP, and determine a TBSaccording to the fixed number of OFDM symbols. Regarding this, the PRBsize scaling method described in Section 4.2.1 or Section 4.2.2 may bereferred to.

The UE may determine that a corresponding SF is the first SF of the TxOPby receiving a reservation signal or an indication by physical layersignaling or higher layer signaling. That is, the UE may consider thatan assumed TBS of 10 OFDM symbols has been applied to the first SF.

In this case, since the number of OFDM symbols in the first SF being apSF is system-determined, there is no need for additional signaling ofthe TBS or the number of OFDM symbols.

4.7.2 TBS Configuration by Signaling

The eNB may configure a variable allocation of 14 OFDM symbols or 10OFDM symbols all the time for the first SF of a TxOP. For example, thelength of a pSF may be configured semi-statically by higher layer signalor dynamically by physical layer signaling (i.e., DCI). For example, theeNB may configure a TBS for a pSF by differentiating a scramblingsequence, a CRS mask, and/or a search space in DCI or adding a new fieldto a DCI format.

The first SF of a TxOP may be configured on the assumption that its TBSis 10 OFDM symbols by higher layer signaling. In this case, uponrecognizing that a corresponding SF is the first SF of the TxOP by areservation signal or an indication received by higher layer signalingor physical layer signaling, the UE may consider that the assumed TBS of10 OFDM symbols is applied to the SF.

Configuring the number of OFDM symbols in a pSF by dynamic signaling(i.e., physical layer signaling, DCI) will be described as anotherexample. In the case where a 1-bit field of a physical layer signal, DCIis used to indicate the number of OFDM symbols, if the field isactivated in the DCI, the UE may determine that an SF carrying the DCIincludes 10 OFDM symbols. Thus, the UE may derive the TBS on theassumption of 10 OFDM symbols in the SF carrying the DCI. On thecontrary, if the field is deactivated in the DCI, the UE may derive theTBS on the assumption that the SF carrying the DCI includes 14 OFDMsymbols.

Accordingly, the UE may decode data transmitted in the pSF based on thederived TBS.

While Section 4.7 deals with a case in which the first SF of a TxOP is apSF, it is applicable in the same manner to a case in which the last SFof a TxOP is a pSF.

4.8 Method for Transmitting and Receiving Data According to TxOPConfiguration

FIG. 31 is a flowchart illustrating one of methods for transmitting andreceiving data according to a TxOP configuration.

Methods for configuring a TxOP to transmit data in an SCell being anunlicensed band by an eNB have been described before in Sections 4.1 to4.7. The eNB may perform a backoff operation and/or a CS operation toconfigure a TxOP in an SCell (S3110).

If a channel of the SCell is determined to be idle through the backoffoperation and/or the CS operation, the eNB may determine an SF structurein order to configure a TxOP (S3120).

For example, if an SF of the SCell is aligned with an SF boundary of aPCell, an SF of the SCell is always configured in the same structure asan SF of the PCell, and thus the eNB and the UE may transmit and receivedata according to an SF configuration defined for the PCell (fordetails, refer to Section 4.1).

To increase a data throughput in the PCell and the SCell, the first SFor the last SF of the TxOP may be configured to be a pSF shorter than anSF of the PCell (for details, refer to Section 4.2 to Section 4.7).

If the first SF and/or the last SF is configured to be a pSF, the eNBmay indicate the number of OFDM symbol or a TBS for the pSF to the UE byhigher layer signaling or physical layer signaling (not shown).

Or if a pSF is configured in the TxOP, the number of OFDM symbols in thepSF may be fixed in the system. In this case, the UE may receive databased on a TBS determined according to the fixed number of OFDM symbols.

Or if a pSF is configured in the TxOP, the eNB may fix the number ofOFDM symbols available for the pSF to a predetermined value (e.g., 2 or3) in order to reduce a processing delay. That is, a pSF may beconfigured with as many OFDM symbols as one of a plurality of numbers ofOFDM symbols based on the number of OFDM symbols available forconfiguring a TxOP in an SF for which CS has been performed. In thiscase, the eNB may indicate the number of OFDM symbols in the configuredpSF to the UE by higher layer signaling or physical layer signaling.

The eNB may transmit data in the configured TxOP and the UE may receivethe data in the TxOP.

The foregoing embodiments of the present disclosure have been describedin the context of DL. However, the embodiments of the present disclosurecan be extended to UL as they are, except that DL RSs are replaced withUL RSs. For example, Section 4.1 and Section 4.4 may be extended as abackoff method for UL transmission, and Section 4.2 may be extended to amethod for determining a TBS for a pSF on UL.

5. Apparatuses

Apparatuses illustrated in FIG. 32 are means that can implement themethods described before with reference to FIGS. 1 to 31.

A UE may act as a transmission end on a UL and as a reception end on aDL. An eNB may act as a reception end on a UL and as a transmission endon a DL.

That is, each of the UE and the eNB may include a Transmitter (Tx) 3240or 3250 and a Receiver (Rx) 3260 or 3270, for controlling transmissionand reception of information, data, and/or messages, and an antenna 3200or 3210 for transmitting and receiving information, data, and/ormessages.

Each of the UE and the eNB may further include a processor 3220 or 3230for implementing the afore-described embodiments of the presentdisclosure and a memory 3280 or 3290 for temporarily or permanentlystoring operations of the processor 3220 or 3230.

The embodiments of the present disclosure may be performed using theafore-described components and functions of a UE and an eNB. Forexample, the eNB may determine whether an SCell is idle by performing abackoff operation and a CS operation. If the SCell is idle, the eNB mayconfigure a TxOP and transmit and receive data during the TxOP. The ENBmay occupy the SCell by transmitting a reservation signal until beforethe configured TxOP. When configuring the TxOP, the eNB may configure apSF and transmit information about the pSF to the UE. The pSF may beconfigured as the first and/or last SF of the TxOP. The UE may determinethe TxOP configuration based on TxOP configuration information and/orthe information about the pSF, and transmit and receive data in theTxOP. For various methods for configuring a TxOP, refer to theembodiments of the present disclosure described in Section 1 to Section4.

The Tx and Rx of the UE and the eNB may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDM packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the eNB of FIG. 32may further include a low-power Radio Frequency (RF)/IntermediateFrequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory3280 or 3290 and executed by the processor 3220 or 3230. The memory islocated at the interior or exterior of the processor and may transmitand receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to various wireless access systemsincluding a 3GPP system, a 3GPP2 system, and/or an IEEE 802.xx system.Besides these wireless access systems, the embodiments of the presentdisclosure are applicable to all technical fields in which the wirelessaccess systems find their applications.

The invention claimed is:
 1. A method performed by a base station in awireless access system, the method comprising: performing a carriersensing procedure to determine whether a cell configured in anunlicensed band is idle; and transmitting, in the cell, a downlinktransmission on one or more consecutive time periods after the cell isdetermined to be idle, wherein a number of symbols, on which at leastpart of the downlink transmission is mapped, included in a last timeperiod among the one or more consecutive time periods is less than 14,wherein information indicating the number of the symbols is transmittedthrough downlink control information, wherein the last time period isincluded in a full time period configured as 14 symbols, and whereinremaining symbols included in the last time period except for thesymbols are unoccupied by transmissions in the unlicensed band.
 2. Themethod of claim 1, wherein the number of the symbols satisfies one of aplurality of downlink pilot time slot (DwPTS) configurations.
 3. Themethod of claim 1, wherein a 1^(st) time period among the one or moreconsecutive time periods starts from a predetermined symbol boundarywithin the full time period, and wherein a size of the 1^(st) timeperiod is equal to or less than the full time period.
 4. The method ofclaim 3, wherein a starting time of the 1^(st) time period is alignedwith a boundary of the full time period, and wherein a symbol within aduration of the downlink transmission is aligned with a symbol of a cellconfigured in a licensed band.
 5. The method of claim 2, wherein theDwPTS configurations are defined as in Table 1, TABLE 1 Normal cyclicprefix in downlink UpPTS Special subframe Normal cyclic prefix Extendedcyclic configuration DwPTS in uplink prefix in uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s) 1 19760 · T_(s) 2 21952 · T_(s) 3 24144 ·T_(s) 4 26336 · T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 6 19760· T_(s) 7 21952 · T_(s) 8 24144 · T_(s) 9 13168 · T_(s)

wherein T_(s) denotes a sampling time.
 6. A method performed by a userequipment in a wireless access system, the method comprising: receivinga downlink transmission in one or more consecutive time periods, whereinthe downlink transmission is received in a cell configured in anunlicensed band after the cell is determined to be idle based on acarrier sensing procedure for determining whether the cell is idle,wherein a number of symbols, on which at least part of the downlinktransmission is mapped, included in a last time period among the one ormore consecutive time periods is less than 14, wherein informationindicating the number of the symbols is received through downlinkcontrol information, wherein the last time period is included in a fulltime period configured as 14 symbols, and wherein remaining symbolsincluded in the last time period except for the symbols are unoccupiedby transmissions in the unlicensed band.
 7. A user equipment configuredto operate in a wireless access system, the user equipment comprising: amemory; and at least one processor operatively coupled to the memory,wherein the at least one processor is configured to: receive a downlinktransmission in one or more consecutive time periods, wherein thedownlink transmission is received in a cell configured in an unlicensedband after the cell is determined to be idle based on a carrier sensingprocedure for determining whether the cell is idle, wherein a number ofsymbols, on which at least part of the downlink transmission is mapped,included in a last time period among the one or more consecutive timeperiods is less than 14, wherein information indicating the number ofthe symbols is received through downlink control information, whereinthe last time period is included in a full time period configured as 14symbols, and wherein remaining symbols included in the last time periodexcept for the symbols are unoccupied by transmissions in the unlicensedband.
 8. A base station configured to operate in a wireless accesssystem, the base station comprising: a memory; and at least oneprocessor operatively coupled to the memory, wherein the at least oneprocessor is configured to: perform a carrier sensing procedure todetermine whether a cell configured in an unlicensed band is idle; andtransmit, in the cell, a downlink transmission in one or moreconsecutive time periods after the cell is determined to be idle,wherein a number of symbols, on which at least part of the downlinktransmission is mapped, included in a last time period among the one ormore consecutive time periods is less than 14, wherein informationindicating the number of the symbols is transmitted through downlinkcontrol information, wherein the last time period is included in a fulltime period configured as 14 symbols, and wherein remaining symbolsincluded in the last time period except for the symbols are unoccupiedby transmissions in the unlicensed band.
 9. The base station of claim 8,wherein a 1^(st) time period among the one or more consecutive timeperiods starts from a predetermined symbol boundary within a full timeperiod configured as 14 symbols, and wherein a size of the 1^(st) timeperiod is equal to or less than the full time period.
 10. The basestation of claim 9, wherein a starting time of the 1^(st) time period isaligned with a boundary of the full time period, and wherein a symbolwithin a duration of the downlink transmission is aligned with a symbolof a cell configured in a licensed band.
 11. The base station of claim8, wherein the number of the symbols satisfies one of a plurality ofdownlink pilot time slot (DwPTS) configurations.
 12. The base station ofclaim 11, wherein the DwPTS configurations are defined as in Table 1,TABLE 1 Normal cyclic prefix in downlink UpPTS Special subframe Normalcyclic prefix Extended cyclic configuration DwPTS in uplink prefix inuplink 0  6592 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 · T_(s) 2 21952· T_(s) 3 24144 · T_(s) 4 26336 · T_(s) 5  6592 · T_(s) 4384 · T_(s)5120 · T_(s) 6 19760 · T_(s) 7 21952 · T_(s) 8 24144 · T_(s) 9 13168 ·T_(s)

wherein T_(s) denotes a sampling time.
 13. The method of claim 1,wherein the information indicating the number of the symbols isinformation only indicating the number of the symbols.